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ISU researchers study insecticide-free method for control of soybean aphids

Posted Sep 15, 2009

AMES, Iowa - Two Iowa State University researchers are
examining a new method of controlling soybean aphids without
the use of chemical pesticides.

Bryony Bonning, professor of entomology, and Allen Miller,
professor of plant pathology and director of the Center for
Plant Responses to Environmental Stresses, are looking at a way
to genetically modify soybeans to prevent damage from aphids.

If the research is successful, soybeans will carry in-plant
protection from aphids, similar to the way genetically modified
corn now keeps the European Corn Borer from destroying corn
yields, but using a different molecular tool. Modified corn
technology has been in use for about 12 years.

The study is being funded by a Grow Iowa Values Fund Grant. The
goal of the grant program is to support development of
technologies with commercial potential and to support the
growth of companies using those technologies.

The researchers are working with Pioneer Hi-Bred, a DuPont
business, as their corporate partner.

Previous research at Iowa State University indicated that if
major soybean aphid outbreaks were left untreated, the loss in
yield could exceed $250 million in Iowa. The annual cost to
prevent the yield loss with insecticides can reach $64 million
for Iowa soybean growers.

Soybean aphid outbreaks have become an annual phenomenon in
Iowa, according to Miller.

The current research focuses on introducing a gene into
soybeans that is harmless to mammals, but creates a toxin that
is lethal to aphids that feed on soybean plants.

In order to be effective, the toxin needs to be taken intact
into the body cavity of the aphid, not broken down by the
digestive system in the bug.

Miller and Bonning identified a plant virus coat protein eaten
by soybean aphids that doesn't break down and goes into the
aphid body cavity intact.

They know the virus coat protein remains intact because the
aphids often spread the virus from plant to plant while they
are feeding.

Coat proteins make up the outer shell of a virus particle.

The researchers devised a method to use virus coat proteins to
their advantage. The researchers have fused their toxin to the
virus' protein coat. Since the protein coat is only part of
the virus to be used, there is no risk of an infectious virus.
Also, the coat protein is from a virus that normally
doesn't infect soybeans.

When the hybrid toxin coat protein is eaten by the aphid, the
fatal toxin should get into the aphid body cavity intact.

"What we thought was, if this (virus) protein has this
ability to be taken up into the aphid (intact), let's take
advantage of that specialization and fuse that to other
proteins that are toxic," said Miller.

In addition to possibly curbing the aphid problem and the yield
loss it causes, there are other benefits to the farmers and the
ecosystems.

"The (potential) economic impact overall is huge,"
said Bonning. "There will be less insecticide use, and
also less fossil fuel used to apply the insecticides."

Also, spraying soybeans with insecticides doesn't just
control the aphids, according to Bonning.

"When you spray, you also control beneficial
insects," said Bonning. "Lady beetles are affected,
for example, and they are a natural enemy of the aphids. So
when the aphids come back to a field after spraying, there
won't be any lady beetles to naturally control the aphid
populations."

Miller adds that if growers spray for aphids and don't
eliminate them all, the aphids simply disperse to other fields,
making the problem worse.

"There are many reasons not to spray, but you can't
tell the growers to stop spraying until you give them an
alternative for soybean aphid management," said
Bonning.

-30-

Contacts

Bryony Bonning, Entomology, (515) 294-1989,
bbonning@iastate.edu

Allen Miller, Plant Pathology, (515) 294-2436,
wamiller@iastate.edu

Dan Kuester, News Service, (515) 294-0704, kuester@iastate.edu

Quote

What we thought was, if this (virus) protein has this ability
to be taken up into the aphid (intact), let's take
advantage of that specialization and fuse that to other
proteins that are toxic.

Allen Miller, Plant Pathology

Quote

The (potential) economic impact overall is huge. There will be
less insecticide use, and also less fossil fuel used to apply
the insecticides.